The present invention relates to methods and apparatuses for providing an automated gas tight seal of an opening. More particularly the present invention relates to a door assembly, such as a gate valve or slit valve, for sealing chambers of a semiconductor device fabrication tool.
Semiconductor wafers are processed within automated fabrication tools comprising a plurality of chambers designated for wafer loading/unloading to and from the tool (i.e., a load lock), wafer transfer, or wafer processing. Typically the environment of each chamber must be selectively isolated from the environments of neighboring chambers to prevent cross contamination, and to enable the various chambers to be maintained at pressures that differ according to the process to be performed therein. Load locks also must be selectively isolated from the environment that exists outside the tool. To achieve such selective isolation, each chamber is provided with a slit through which wafer handlers extend to transport wafers to and from the chamber. The slit is selectively sealed with a moveable door (typically referred to as a slit valve for vacuum applications, and as a gate valve for non-vacuum applications). Conventional moveable door assemblies are bulky, consuming valuable clean room space, require many moving parts and frequent replacement. Moveable door assemblies therefore constitute a significant expense.
Many commonly used door assemblies are paddle shaped, having a sealing surface and having an elongated shaft portion that extends downward from the sealing surface. In operation the door assembly is elevated such that the sealing surface occludes the slit opening to be sealed. Thereafter, air cylinders located on the lower-shaft portion of the door assembly are actuated. The air cylinders push against the chamber wall, and thus simultaneously force the lower-shaft portion of the door away from the chamber, and force the sealing surface of the door assembly inward to seal the slit. Over time this cantilevering force bends the shaft, destroying any gas-tight seals located therealong. Further, the sealing surface moves toward the slit opening in a slightly arcing motion which causes the sealing surface to slide along the surface surrounding the slit. This sliding contact generates particles which may contaminate wafer surfaces.
Accordingly, these conventional door assemblies are bulky, expensive, unreliable and generate potentially destructive particles. A need therefore exists for an improved door assembly that is smaller, less expensive, more reliable, and that generates fewer particles than conventional door assemblies.
The present invention provides a moveable door assembly for selectively sealing an opening such as a slit opening of a semiconductor fabrication tool. The door assembly comprises a frontplate adapted to sealingly engage a surface having an opening to be sealed, a backplate operatively coupled to the frontplate, and at least one inflatable member located between the frontplate and the backplate for selectively moving the frontplate into sealing engagement with the opening. The frontplate has a sealing member to effect a gas tight seal around the opening. The frontplate is parallel to the surface having the opening to be sealed, and the inflatable member is coupled so as to move the frontplate in a direction normal to the surface to be sealed. In this manner, the inventive door assembly seals the opening without sliding along the surface which surrounds the opening, and without generating particles thereby.
When the inventive door assembly is configured for use in vacuum environments, the inflatable member comprises one or more vacuum grade members such as bellows made of stainless steel. In an embodiment preferred for vacuum applications, the inventive door assembly is housed within a pocket which is in communication with the opening to be sealed (e.g., within a pocket machined in the outer walls of a central chamber for transferring wafers). The door assembly has a movable mechanism for moving the door to and from a closed position wherein the door assembly occludes the opening. A sealing plate is coupled to the moveable mechanism, and is positioned to seal against the walls of the pocket, thereby creating a gas tight region within the pocket. By pressurizing the gas tight region, after sealing commences, the door assembly""s seal is enhanced (due to the pressure gradient between the gas tight region and the chamber), and a smaller less expensive inflatable member may be employed.
Further advantages are achieved by employing a module having a plurality of bellows coupled to a single gas delivery line which passes through each bellows. Such a design allows the inflatable members and the gas delivery line to be easily replaced or repaired, and renders the design easily scaleable.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.